Multi-ply planar absorbent product and process for manufacturing such a product

ABSTRACT

Adhesive (a 1 , a 2 ) as a pattern of deposits is applied on both sides of a hydrophilic spunbond non-woven inner ply (B) of low grammage and no or low adhesion ability. Together with this inner ply (B) a three ply planar absorbent product is made with tissue outer plies (A,C) by exerting pressure on the adhesive such that the adhesive penetrates through the inner ply (B) for achieving ply bonding between the inner ply (B) and the opposite outer ply (C). The different adhesive patterns do not disturb each other because they do not coincide.

FIELD OF THE INVENTION

The invention relates to multi-ply planar absorbent products and especially 3-plies products made of plies of tissue paper and non-wovens.

BACKGROUND OF THE INVENTION

The term non-woven (ISO 9092, DIN EN 29092) is applied to a wide range of products which, in terms of their properties, are located between those of paper (cf. DIN 6730, May 1996) and cardboard (DIN 6730) on the one hand, and textiles on the other hand. As regards non-woven a large number of extremely varied production processes are used, such as the air-laid and spun-laced techniques as well as wet-laid techniques. The non-woven includes mats, non-woven fabrics and finished products made thereof. Non-wovens may also be called textile-like composite materials, which represent flexible porous fabrics that are not produced by the classic methods of weaving warp and weft or by looping. In fact, non-wovens are produced by intertwining, cohesive or adhesive bonding of fibres, or a combination thereof. The non-woven material can be formed of natural fibres, such as cellulose or cotton fibres, but can also consist of synthetic fibres, such as Polyethylene (PE), polypropylene (PP), polyurethane (PU), polyester, nylon or regenerated cellulose, or a mix of different fibres. The fibres may, for example, be present in the form of endless fibres of pre-fabricated fibres of a finite length, as synthetic fibres produced in situ, or in the form of staple fibres. The nonwovens according to the invention may thus consist of mixtures of synthetic and cellulose fibrous material, e.g. natural vegetable fibres (see ISO 9092, DIN EN 29092).

A tissue paper is defined as a soft absorbent paper having a low basis weight. One generally selects a basis weight of 8 to 30 g/m², especially 10 to 25 g/m² per ply. The total basis weight of multiple-ply tissue products is preferably equal to a maximum of 65 g/m², more preferably to a maximum of 50 g/m². Its density is typically below 0.6 g/cm³, preferably below 0.30 g/cm³ and more preferably between 0.08 and 0.20 g/cm³.

The production of tissue is distinguished from paper production by the its extremely low basis weight and its much higher tensile energy absorption index (see DIN EN 12625-4 and DIN EN 12625-5). Paper and tissue paper also differ in general with regard to the modulus of elasticity that characterizes the stress-strain properties of these planar products as a material parameter.

A tissue's high tensile energy absorption index results from the outer or inner creping. The former is produced by compression of the paper web adhering to a dry cylinder as a result of the action of a crepe doctor or in the latter instance as a result of a difference in speed between two wires (“fabrics”). This causes the still moist, plastically deformable paper web to be internally broken up by compression and shearing, thereby rendering it more stretchable under load than an uncreped paper.

Moist tissue paper webs are usually dried by the so-called Yankee drying, the through air drying (TAD) or the impulse drying method.

The fibers contained in the tissue paper are mainly cellulosic fibres, such as pulp fibers from chemical pulp (e.g. Kraft sulfite and sulfate pulps), mechanical pulp (e.g. ground wood), thermo mechanical pulp, chemo-mechanical pulp and/or chemo-thermo mechanical pulp (CTMP). Pulps derived from both deciduous (hardwood) and coniferous (softwood) can be used. The fibers may also be or include recycled fibers, which may contain any or all of the above categories. The fibers can be treated with additives—such as fillers, softeners, such as quaternary ammonium compounds and binders, such as conventional dry-strength agents or wet-strength agents used to facilitate the original paper making or to adjust the properties thereof. The tissue paper may also contain other types of fibers, e.g. regenerated cellulosic fibres or synthetic fibers enhancing, for instance, strength, absorption, smoothness or softness of the paper.

Tissue paper may be converted to the final tissue product in many ways, for example, by embossing or laminating it into a multi-ply product, rolled or folded.

If tissue paper is to be made out of pulp, the process essentially comprises

-   a forming that includes the headbox and the forming wire portion, -   b the drying portion (TAD (through air drying)) or conventional     drying on the yankee cylinder) that also usually includes the crepe     process essential for tissues, -   c typically the monitoring and winding area.

Paper can be formed by placing the fibers, in an oriented or random manner, on one or between two continuously revolving wires of a paper making machine while simultaneously removing the main quantity of water of dilution until dry-solids contents of usually between 12 and 35% are obtained.

Drying the formed primary fibrous web occurs in one or more steps by mechanical and thermal means until a final dry-solids content of usually about 93 to 97%. In the case of tissue making, this stage is followed by the crepe process which crucially influences the properties of the finished tissue product in conventional processes. The conventional dry crepe process involves creping on a usually 4.5 to 6 m diameter drying cylinder, the so-called yankee cylinder, by means of a crepe doctor with the aforementioned final dry-solids content of the raw tissue paper (wet creping can be used if lower demands are made of the tissue quality). The creped, finally dry raw tissue paper (raw tissue) is then available for further processing into the paper product or tissue paper product according to the invention.

Instead of the conventional tissue making process described above, the use of a modified technique is possible in which an improvement in specific volume is achieved by a special kind of drying within process section b and in this way an improvement in the bulk softness of the thus made tissue paper is achieved. This process, which exists in a variety of subtypes, is termed the TAD (through air drying) technique. It is characterized by the fact that the “primary” fibrous web (like a non-woven) that leaves the forming and sheet making stage is pre-dried to a dry-solids content of about 80% before final contact drying on the yankee cylinder by blowing hot air through the fibrous web. The fibrous web is supported by an air-permeable wire or belt (or TAD-fabric) and during its transport is guided over the surface of an air-permeable rotating cylinder drum (TAD-cylinder). Structuring the supporting wire or belt makes it possible to produce any pattern of compressed zones broken up by deformation in the moist state, also named moulding, resulting in increased mean specific volumes and consequently leading to an increase in bulk softness without decisively decreasing the strength of the fibrous web. Such a pattern is fixed in the area of the TAD-cylinder. Thereafter the pattern is further imprinted between the TAD-fabric and the Yankee-cylinder.

Creping may be conducted also during transfer of the paper sheet from the forming wire directly to the TAD-fabric or via a transfer fabric. For this creping the formingfabric runs faster than the following fabric receiving the sheet (rush transfer). For example, when applying the TAD technique for the production of raw tissue and the usual double-screen sheet formation in c-wrap configuration, for example, the so-called inner sheet-forming screen can thus be operated at a speed that is up to 40% faster than that of the next fabric or that of the subsequent felt, the initially formed and already pre-drained paper web being transferred to the next TAD fabric. This causes the still moist and as a result plastically deformable paper web to be internally broken up by compression and shearing, thereby rendering it more stretchable under load than a paper that has undergone neither “internal” nor external creping. This transfer of still plastically deformable paper web at a differential speed that simultaneously takes effect may also be brought about in other embodiments between a transfer fabric and the so-called TAD imprinting fabric or between two transfer fabrics.

Another possible influence on the softness and strength of the raw tissue lies in the production of a layering in which the primary fibrous web to be formed is built up by a specially constructed headbox in the form of physically different layers of fibrous material, these layers being jointly supplied as a pulp strand to the sheet making stage.

When processing the raw fibrous web or raw tissue paper into the final product (third process section), the following procedural steps are normally used individually or in combination: cutting to size (longitudinally and/or cross cutting), producing a plurality of plies, producing mechanical ply adhesion, volumetric and structural embossing, ply adhesion, folding, imprinting, perforating, application of lotions, smoothing, stacking, rolling up.

To produce multi-ply tissue paper products, such as handkerchiefs, toilet paper, towels or kitchen towels, an intermediate step preferably occurs with so-called doubling in which the raw tissue in the finished product's desired number of plies is usually gathered on a common multiply master roll.

The processing step from the raw tissue that has already been optionally wound up in several plies to the finished tissue product occurs in processing machines which include operations such as repeated smoothing of the tissue, edge embossing, to an extent combined with full area and/or local application of adhesive to produce ply adhesion of the individual plies (raw tissue) to be combined together, as well as longitudinal cut, folding, cross cut, placement and bringing together a plurality of individual tissues and their packaging as well as bringing them together to form larger surrounding packaging or bundles. The individual paper ply webs can also be pre-embossed and then combined in a roll gap according to the foot-to-foot or nested methods.

Hygiene or wiping products primarily include all kind of dry-creped tissue paper, wet-creped paper and cellulose or pulp wadding or all kinds of non-wovens, or combinations, laminates or mixtures thereof. Typical properties of these hygiene and wiping products include the ready ability to absorb tensile stress energy, their drapability, good textile-like flexibility, properties which are frequently referred to as bulk softness, a high surface softness, and a high specific volume with a perceptible thickness. As high a liquid absorbency as possible and, depending on the application, a suitable wet and dry strength as well as an appealable visual appearance of the outer product surface is desired. These properties, among others, allow these hygiene and wiping products to be used, for example, as cleaning wipes such as paper or non-woven wipes, windscreen cleaning wipes, industrial wipes, kitchen paper, or the like; as sanitary products such as for example toilet paper, paper or non-woven handkerchiefs, household towels, towels, and the like; as cosmetic wipes such as for example facials and as serviettes or napkins, just to mention some of the products that can be used. Furthermore, the hygiene and wiping products can be dry, moist, wet or pre-treated in any manner. In addition, the hygiene and wiping products may be folded, interleaved or individually placed, stacked or rolled, connected or not, in any suitable manner.

Due to the above description, the products can be used for personal and household use as well as commercial and industrial use. They are adapted to absorb fluids, for decorative purposes, for packaging or even just as supporting material, as is common for example in medical practices or in hospitals. In terms of their wide variety, hygiene and wiping products are now considered to be everyday products.

From WO 01/36188 A is known a multi-ply absorbent disposable surgical textile, especially a multi-ply absorbent wipe, comprising at least a first and a second outer non-woven ply, and at least one inner film bonded together with adhesive means. The inner film is a thermoplastic copolyester elastomer and a first pattern of discrete adhesive deposits is present on one side of the inner film and a second pattern of discrete adhesive deposits is present on the other side of the inner film, wherein said second pattern at least partly does not coincide with the first pattern. In this document is well described a method of making such multi-ply absorbent structure in which the patterns of discrete adhesive deposits are applied on each side of the inner film, followed by placing the outer plies on said inner film and pressing them.

From WO 96/24485 A1 multi-ply paper laminates are known using controlled adhesive strike-through. A carrier sheet of synthetic spunbond non-woven having suitable airflow characteristics is covered on each side with the less open paper without strike-through. The adhesive is applied in a pattern on one side of the carrier sheet. This laminate is a especially suited for paper products such as disposable table napkins.

U.S. Pat. No. 3,958,055 A1 teaches adhesive bonding of isotropic fiber webs to form pattern bonded composites. The process for manufacturing a non-woven fabric in a single path involves printing the adhesive on one web of cellulosic tissue in a clearly defined fine line pattern, laying the fiber web on the adhesive bearing surface of the tissue web, disposing a second cellulosic tissue web on the fiber web, and hot calendering the three layer composite so as to force the adhesive through the fiber web into the second tissue web while bonding the fibers of reinforcing web in place.

From U.S. Pat. No. 3,650,882 A1 is known a multi-ply paper towel comprising for example three tissue plies. The adhesive is applied either to the inner surface of the outer plies or on both sides of the inner ply in order to achieve ply-bonding between the inner ply and each of the outer plies.

Furthermore, from EP 0679122 B1, EP 0564319 B1 and EP 1017563 B1 a laminated fibrous structure is known comprising at least three tissue plies, wherein the adhesive is applied on each inner surface of the outer plies in order to achieve ply-bonding between each of the outer plies and the inner ply.

SUMMARY OF THE INVENTION

It is the technical problem of the invention to provide a multi-ply planar absorbent product and especially a toilet paper or household towel and the like with good ply-bonding especially when an inner ply is used, which is made of a material of low-adhesion ability. “Adhesion Ability” is the ability of a material to bind with another one using a given adhesive and resulting in a ply bonding of an acceptable level. A ply bonding of an acceptable level for tissue products is in a range between 0.08 and 0.3 N/50 mm (measured on a dry material, on the machine direction/mean value of the peaks above the total mean value).

This problem is solved by a multi-ply planar absorbent product, which comprises at least a first and a second outer tissue ply and at least one inner non-woven ply bonded together, with an adhesive, wherein the inner ply is a material of no or low adhesion ability. A first adhesive is present on one side of the inner ply in a first pattern of discrete adhesive deposits and a second adhesive is present on the other side of the inner ply in a second pattern of discrete adhesive deposits, wherein said second pattern at least partly does not coincide with the first pattern. Each of the first and second adhesive penetrates through the inner ply thereby bonding together the inner ply and at least the outer ply on the side opposite to the side where the adhesive is applied.

Preferably at least one of the plies is embossed either separately or in unison. Especially both of the outer plies are embossed and the embossment can be such that sandwiching the inner ply, the outer plies are in “foot-to-foot” contact wherein the adhesive is present at least in some of the “foot-to-foot” areas. If steel rolls are used for embossing in these “foot-two-foot” areas, the necessary pressure is achieved and applied on the adhesive.

According to a further improvement the embossment is such that sandwiching the inner ply, the outer plies are in “nested” contact wherein the adhesive is present in at least some of the “nested” areas. Preferably the adhesive surrounds mechanically fibers of the inner ply according to an interlocking grip. Together therewith the material of the non-woven inner ply can be a hydrophilic material. Especially the material is hydrophilic spunbond of low grammage. Therewith the tissue of the outer plies may be a through-air-dried (TAD) paper of about 18 g/m² and the material of the inner ply then might be a hydrophilic spunbond non-woven of low grammage of about 9 gsm.

Furthermore, the problem is solved by a process for manufacturing a multi-ply planar absorbent product, which comprises at least a first and a second outer tissue ply and at least one inner non-woven ply made of a material of low adhesion ability bonded together, with an adhesive, said process comprising the steps of applying adhesive on one side of the inner ply in a first pattern of discrete adhesive deposits, applying adhesive on the other side of the inner ply in a second pattern of discrete adhesive deposits wherein said second pattern at least partly does not coincide with the first pattern. Then the first and the second tissue plies are placed on those sides of the inner ply carrying the first second pattern of adhesive respectively. Afterwards the plies are pressed together at least in those areas carrying the discrete adhesive deposits to cause them to penetrate through the inner ply thereby bonding together at least the inner ply and the ply lying opposite to the application side of the respective adhesive deposit.

By the invention a product is achieved in which in an easy manner, an appropriate ply bonding can be achieved when the inner ply is of no or low adhesion ability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described hereafter on the basis of the following drawings illustrating some embodiments according to the present invention.

FIG. 1 shows the principle of ply-bonding a three-ply product.

FIG. 2 a to FIG. 2 d show the steps of manufacturing a three-ply planar absorbent product.

FIG. 3 to FIG. 5 show in three steps how adhesive penetrates through an inner ply in order to achieve ply-bonding on the other side.

FIG. 6 to FIG. 8 show different modes of manufacturing a three-ply product with different modes of applying.

DETAILED DESCRIPTION OF THE INVENTION

As an example a three-ply product is described. These are the plies A, B and C. The plies A and C are named the outer plies and the ply B the inner ply. As an example the outer plies are made of a material being 18 g/m² TAD (through air-dried) tissue paper. The material of the inner ply B is for example spunbond hydrophilic low grammage non-woven of 9 gsm. Such a non-woven has a low adhesion ability especially when the fiberes are covered by a surfactant. For instance as non-woven is used a 100% Polypropylene based hydrophilic spunbond (supplied from Supplier Union, 9 gsm, reference S0900PPW).

For example the non-woven is hydrophilic due to application of a surfactant while producing it.

In the following description an embodiment is shown where an adhesive is used for ply-bonding.

In FIG. 1 is illustrated the application of drops of adhesive al on one side 1 of the inner ply B. On the other side 2 of the inner ply B also drops of adhesive a2 are applied. In this way patterns of adhesive drops are applied to the inner ply B in such a manner that the patterns do not coincide. By the adhesive ply-bonding is achieved between the plies and especially between ply A and B and ply C and B. By the adhesive a2 a ply-bonding is achieved between ply B and ply A and by the adhesive al between the ply B and the ply C. The reason is that the material of the inner ply B is in this example spunbond hydrophilic non-woven of low grammage having a low adhesion ability so that by the adhesive a2 no or poor ply-bonding can be achieved between the inner ply B and the outer ply C. The non-woven used is (supplied from supplier UNION, 9 gsm, refernce SO900PPW) a 100% Polypropylenne based hydrophilic spunbond. In this case the non-woven is hydrophilic due to the application of a surfactant while producing it.Under adhesion ability is to be understood the ability of a material to bind with another one using a given adhesive and resulting in a ply bonding of an acceptable level. A ply bonding of an acceptable level for tissue production is in a range between 0.08 and 0.3 N/50 mm (average of peaks on dry material in the machine direction).Therefore, by pressure application the adhesive a2 penetrates the inner ply B and is interlocked between the fibers and the adhesive extending to the side 1 of the inner ply B forms a ply-bonding with the outer ply A having a high adhesion ability. The same happens with the adhesive a1 in the opposite manner. The adhesive used is “SWIFT L 998/4”, a Polyvinylacohol and Polyethyleneglycol based adhesion of a viscosity being 18000 mPa at 26° C.

The manufacturing process as a principle is illustrated in FIG. 2 a to FIG. 2 d. According to FIG. 2 a in the before mentioned manner the adhesive is applied on two sides of the inner ply B by an application tool 3 and 4. The result is visible from FIG. 2 b. In this step the inner ply B is brought together with the plies A and C. According to the illustration in FIG. 2 c the three-ply configuration, for instance as a continuous web is fed into the operation area of a pressure-marrying tool 5 and 6. The pressure is exerted according to the arrows 7 to locations where the adhesive is present so that the pressure is exerted not only on the plies but also on the adhesive. The result after exerted pressure is illustrated in FIG. 2 d, which shows the well known “foot-to-foot” configuration, which could also be a so called and well known “nested”-configuration.

By the pressure exerted on the adhesive the adhesive penetrates through inner ply B in order to be fixed there so that the adhesive penetrated through the inner ply B causes ply-bonding with the adjacent outer ply being of tissue paper having a high adhesion ability.

The adhesive used herein may be for instance BVOH adhesive of high dry content (Atesin 1900, 16% for instance, Henkel-Polyvinyl Acetate Dispersion). Another adhesive is Polyvinyl alcohol and Plyethylenglycol based (SWIFT L998/4). It has a viscosity of 18.000 mPas at 26° C.

FIG. 3 shows the three-ply configuration with an adhesive drop al applied to the one side one of the inner ply B. According to FIG. 4 pressure is applied to the adhesive drop via the outer tissue ply A. This causes the adhesive drop al to penetrate through the inner ply B such that an adhesive head h is formed by an interlocking grip within the fiber configuration of the inner ply B fixing the adhesive mechanically within the inner ply B. Some adhesive is pressed through the inner ply B to extend by a “tail” t in the direction of the inner side of the outer ply C where it sticks to the inner side of the outer ply C being of material having a high adhesion ability.

The manufacturing principle is more detailed illustrated in three embodiments shown in FIG. 6, FIG. 7 and FIG. 8. According to FIG. 6 the inner ply B runs through application rollers 8 and 9 of application tools 3 and 4 for applying the adhesive a1 and a2 from opposite sides on the inner ply sheet B. Thereafter the such prepared inner ply B is guided together with the outer plies A and C through pressure-marrying rolls 5, 6. At the locations 10 and 11 between the rolls 5 and 12 and the rolls 6 and 13 the outer plies A and C are embossed. In general marrying—and embossing rolls and also applicator rolls are known in this technical field so that it is not necessary here to describe these means more in detail. Downstream the rolls 5 and 6 the final product B as a three-ply planar absorbent product.

Embodiments different from the one illustrated in FIG. 6 an illustrated in FIG. 7 and FIG. 8. There are provided in running direction spaced application tools 3 and 4 for applying the adhesive on the inner ply B. Downstream thereof the inner ply B is combined with the outer plies A and C between the pressure-marrying rolls 5 and 6. According to FIG. 8 in the embossing stations 10 and 11 the outer plies A and C are embossed and probably applied with additional adhesive by the application rolls 14, 15. 

1. Multi-ply planar absorbent product, which comprises at least a first (A) and a second (C) outer tissue ply and at least one inner non-woven ply (B) bonded together, with an adhesive, wherein the inner ply (B) is a material of no or low adhesion ability; a first adhesive is present on one side of the inner ply (B) in a first pattern of discrete adhesive deposits (al); a second adhesive is present on the other side of the inner ply in a second pattern of discrete adhesive deposits (a2), wherein said second pattern at least partly does not coincide with the first pattern; and each of said first and second adhesive penetrates through the inner ply (B) thereby bonding together the inner ply (B) and at least the outer ply (A;C) on the side opposite to the side where the adhesive is applied.
 2. Multi-ply planar absorbent product according to claim 1, wherein at least one of the plies is embossed either separately or in unison.
 3. Multi-ply planar absorbent product according to claim 1, wherein both of the outer plies (A,C) are embossed.
 4. Multi-ply planar absorbent product according to claim 3, wherein the embossment is such that sandwiching the inner ply (B), the outer plies (A,C) are in “foot-to-foot” contact, and the adhesive is present at least in some of the “foot-to-foot” areas.
 5. Multi-ply planar absorbent product according to claim 3, wherein the embossment is such that sandwiching the inner ply (B), the outer plies (A,C) are in “nested” contact, and the adhesive is present in at least some of the “nested” areas.
 6. Multi-ply planar absorbent product according to claim 1, wherein the adhesive mechanically surrounds fibers of the inner ply (B) according to an interlocking grip.
 7. Multi-ply planar absorbent product according to claim 1, wherein the material of the non-woven inner ply (B) is a hydrophilic material.
 8. Multi-ply planar absorbent product according to claim 7, wherein the material is a hydrophilic spunbond of low grammage.
 9. Multi-ply planar absorbent product according to claim 1, wherein the tissue of the outer plies (A,C) is a through-air-dried (TAD) paper of substantially 18 g/m², and the material of the inner ply (B) is a hydrophilic spunbond non-woven of low grammage of substantially 9 gsm.
 10. Process for manufacturing a multi-ply planar absorbent product, which comprises at least a first and a second outer tissue ply and at least one inner non-woven ply made of a material of low adhesion ability bonded together with an adhesive, said process comprising the steps of: applying adhesive on one side of the inner ply in a first pattern of a discrete adhesive deposits; applying adhesive on the other side of the inner ply in a second pattern of discrete adhesive; deposits, wherein said second pattern at least partly does not coincide with the first pattern; placing the first and second tissue plies on those sides of the inner ply carrying the first and second pattern of adhesive respectively; and pressing together the plies at least in those areas carrying the discrete adhesive deposits to cause them to penetrate through the inner ply, thereby bonding together at least the inner ply and the ply lying opposite to the application side of the respective adhesive deposit. 